PROJECT SUMMARY There is a fundamental gap in understanding how to provide prosthetic limbs with intuitive afferent somatosensory feedback essential for interaction with the environment while simultaneously providing efferent motor signals for prosthetic control. Continued existence of this gap represents an important problem because, until it is solved, development of an ideal patient-prosthetic interface which allows for both natural feeling of the prosthetic device and motor control will continue to lead to non-use and abandonment of artificial limbs. The composite regenerative peripheral nerve interface (C-RPNI) is a novel surgical strategy to overcome this problem. The C-RPNI is composed by surgically implanting the distal end of a transected peripheral nerve in between an autogenous free muscle and dermal skin graft. The long-term goal of this research is to develop a single biologic interface where we can record from C-RPNIs to provide high fidelity motor control of a prosthetic limb, while simultaneously stimulating the dermal component of the C-RPNI to provide sensory feedback from the device. The overall objective is for the successful facilitation of a closed-loop sensorimotor control system necessary for ideal prosthetic function. The central hypothesis is that mixed sensorimotor nerves will demonstrate preferential motor reinnervation of muscle and sensory reinnervation of skin in the C-RPNI, and that these constructs will remain electrophysiologically stable over time. Guided by strong animal and human preliminary data in the applicant's laboratory, this hypothesis will be tested by pursuing two specific aims: 1) Detailed histologic analysis to characterize: (i) tissue viability (ii) regeneration, and (iii) selective motor and sensory organ reinnervation of the C-RPNI by a mixed nerve, and; 2) Determine electrophysiological signal transduction capabilities of both dermal and muscle C-RPNI components following electrical stimulation. Under the first aim, direct evaluation of C-RPNI vascularity, reinnervation, presence or absence of neuroma, inflammation, and atrophy will be characterized. Selective motor and sensory axon reinnervation in target tissues will confirm selective reinnervation of the muscle and skin components in C-RPNI constructs. Under the second aim, an already proven in situ and in vivo preparation, which has been established feasible in the applicants' hands, will be used to evaluate physiologic segregation of motor and sensory signals in C-RPNIs. The approach is innovative, in the applicant's opinion, because it departs from the status quo by providing both muscle and dermal components for mixed sensorimotor nerves to regenerate into. The proposed research is significant, because results are expected to vertically advance understanding of intuitive prosthetic control, while providing the basis for closed-loop neural control of prosthetic systems. Successful development and safe implementation of this peripheral nerve interface technology would cultivate the evolution of a system with ideal prosthesis function.